Selective Chromium(VI) Trapping by an Acetate-Releasing Coordination Polymer.

Area of Science:

• Materials Science
• Environmental Chemistry
• Coordination Chemistry

Background:

• Hexavalent chromium (Cr(VI)) is a toxic environmental pollutant requiring efficient removal methods.
• Coordination polymers offer potential as adsorbents due to their tunable structures and high surface areas.
• Existing Cr(VI) removal technologies often face limitations in capacity, selectivity, or operational conditions.

Purpose of the Study:

• To investigate the Cr(VI) uptake capacity and selectivity of the coordination polymer silver bipyridine acetate (SBA).
• To characterize the structural changes and product phases formed during Cr(VI) capture by SBA.
• To evaluate the performance of SBA under various pH conditions and in the presence of competing anions.

Main Methods:

• Synthesis of silver bipyridine acetate (SBA) via a one-step, room temperature aqueous method.
• Batch adsorption experiments to determine Cr(VI) uptake capacity and selectivity across a pH range (2-10).
• Structural characterization of SBA and the resulting chromium-containing product phases (SBC and SBDC) using X-ray diffraction.
• Competitive adsorption studies with excess sulfate, nitrate, and carbonate anions.

Main Results:

• SBA exhibits high Cr(VI) uptake capacity, reaching a maximum of 143 mg Cr/g at pH 4.
• The Cr(VI) capture process involves the release of acetate and formation of silver bipyridine chromate (SBC) and dichromate (SBDC) phases.
• SBA maintains >97% Cr(VI) removal efficiency in the presence of a 50-fold molar excess of sulfate, nitrate, or carbonate.
• SBA demonstrates superior Cr(VI) sequestration compared to silver 1,2-bis(4-pyridyl)ethane nitrate (SEN).

Conclusions:

• Silver bipyridine acetate (SBA) is a highly effective and selective adsorbent for removing Cr(VI) from aqueous solutions.
• SBA offers advantages including simple synthesis, high capacity, broad pH applicability, and selectivity over common anions.
• The non-toxic acetate anion released during capture makes SBA an environmentally benign Cr(VI) remediation material.